Belt development electrode



July 22, 1958 Filed June 16, 1955 E. HAYFORD BELT DEVELOPMENT ELECTRODE 2 Sheets-Sheet 1 HIGH VOLTAGE SOURCE VACUUM C LEANER DEVELOPER CLOUD SUPPLY VACUUM CLEANER IN VEN TOR.

RICHARD E. HAYFORD Y QMMEW ATTORNEY July 22, 1958 E. HAYFORD 2,844,123

- BELT DEVELOPMENT ELECTRODE Filed June 16, 1955 2 SheetsSheet 2 Fig. 5

NEGATIVE.

PRESSURE PRESSURE GENERATOR v INVENTOR. RlCHARD E. 'HAYFORDI BY ATTORNEY BELT DEVELGPWNT ELECTRQDE.

Richard E. Hayford, Pittst'ord, N. Y., assignor to Haloid Xerox Inc., Rochester, N. Y., a corporation of New York Application June 16, 1955, Serial No. 515,855

8 Claims. (Cl. 113637) This invention relates in general to xerography and more particularly to an electrode used in the development process.

In xerography, plates composed of photoconductive insulating materials overlying a conductive backing member are sensitized by placing a uniform electrostatic charge on the surface of the photoconductive insulating layer while the plate is kept in darkness, and a latent image is formed on the surface of the insulating layer by exposing this layer, while sensitive, to a light pattern. Exposure to light causes areas of the photoconductive insulating layer to become conductive and charges on the surface are dissipated. Areas not exposed to light continue to act as insulators and, thus, retain their electrostatic charges. The electrostatic charge pattern formed after exposure of the sensitive plate may be developed by bringing electrostatically charged particles into contact with the surface area carrying the charge pattern, or the pattern may be otherwise utilized. A developed image composed of particles deposited in conformity with the electrostatic charge pattern may be transferred from the surface of the plate to sheets or webs through the use of electrostatics or other methods known to the art and may be there permanently affixed.

Xerography may be adapted for automatic operation by cycling the xerographic plate through the difierent steps necessary to produce a developed image, which then may be transferred. The cycle to produce the developed and transferred image may be repeated automatically.

A problem which has been encountered in automatic continuously operating machines involves an electrode used during the development stage when quality prints are desired. This electrode, which will be referred to in this application as a development electrode is closely positioned at a spaced distance from the photoconductive insulating layer during development.

Basic to the use of the development electrode is the desire to reproduce copies of high quality and without distortion of the original image. Electrostatic lines of force exist between the electrostatic charges on the photoconductive insulating layer and areas of different charge potential. When large areas carrying electrostatic charges exist the lines of force which are present due to charges in the central area of the large area tend to run inward through the photoconductive insulating layer to the conductive backing member which is the nearest surface carrying a different potential. Lines of force running from electrostatic charges near the external boundaries of this large area will tend to extend outward and around the outside border of the large area at which point their paths will extend inward to the photoconductive insulating layer to an area carrying a different potential. Development of such an electrostatic image creates deposition which relates to the paths taken by the electrostatic lines of force or development of the electrostatic fields. Therefore, development of a large area as has just been described will reproduce copies with hollow centers and emphasized edges. To prevent such development a surface is positioned at a slight distance from the photoconductive insulating layer during development. This surface, the development electrode, is composed of a conductive material and is either biased or maintained at the potential found on the plate backing member. Such an equipotential surface will cause an increase in the lines of force extending outwardly from the plate member creating electrostatic fields which when developed will produce distortion free and fringe free high quality copy.

During development fine charged powder particles are brought into the field of influence of the charges on the surface and are deposited on charged areas. The development electrode which is spaced at a slight distance from the sensitive layer, tends to build up on its surface a coating of developer material. While this coating remains thin the image which is developed is generally not affected. However, a coating of developer material on the development electrode interposes a new surface between the sensitive layer and the development electrode. If the particles carry electrostatic charge, this coating may effectively change the bias potential on the electrode which substantially decreases beneficial aspects of the development electrode during development. This coating also adds additional and uncontrollable problems. The lack of control which follows heavy deposition is to some extent attributed to the fact that the coating which forms is generally uneven and follows unknown and different patterns. A heavy coating may drop agglomerates of developer powder to the plate surface resulting in a nonuniform distorted development of the electric image pattern. Also, such a coating may cause irregular and uncontrolled fiow patterns of the developer material being presented to the plate surface which will cause streaking of the developed image.

In continuously operating automatic machines, development is constantly taking place, in that a new portion of a plate carrying an electrostatic charge pattern is con tinuously presented to the development zone for development purposes. It, therefore, becomes desirable to present a development electrode above the area to be developed with a minimum coating of developer particles to facilitate high quality true reproductions in continuously operating automatic machines.

It is an object of this invention to improve the art of Xerography by providing new means, methods and apparatus which relate to the development electrode.

It is a further object of this invention to devise and disclose mechanism to provide for presentation of a development electrode carrying a minimum coating of developer particles over areas to be developed in a development zone on a xerographic machine.

It is yet a further object of this invention to provide new methods to clean all areas of the development electrode used in a machine adapted for continuous operation during each successive cycle of movement of the development electrode.

Other objects and advantages of this invention will be apparent in view of the following description considered in the light of the attached drawings wherein:

Fig. 1 is a schematic view of one embodiment of an automatic electrophotographic device adapted for continuous operation.

Fig. 2 is a diagrammatic view of one embodiment of the development zone.

Fig. 3 is a cross sectional view taken along line 33 of Fig. 2.

Fig. 4 is another embodiment showing schematically the development electrode positioning mechanism.

Pig. 5 is yet another embodiment showing schematically the development electrode positioning mechanism.

Fig. 6 is another embodiment of a xerographic automatic machine wherein the plate is flexible.

Fig. 7 is an embodiment of a development electrode according to this invention having guide means attached.

Fig. 8 is a cross sectional view of one embodiment of the guide means of Fig. 7 positioned in a guide path.

Fig. 9 is one embodiment of the shape of the guide path.

Referring more specifically to the drawings, in F1g. 1 an embodiment of a continuously operating xerograph c apparatus is shown. The xerographic plate is, in th1s instance, formed in the shape of a rotating drum generally designated 10 and is composed of conductive backing member 11 and photoconductive insulating layer 12. Conductive backing member 11 is, as indicated, held at a ground potential. A uniform electrostatic charge is placed on layer 12 by corona discharge electrode 13, which is supplied from high voltage source 15 at the area generally designated 25. It is to be realized, of course, that other means for placing an electrostatic charge on this surface may be used and are intended to be encompassed by this invention. An image l6 moving at a proper linear speed is illuminated by lamps l7 and is projected from slit 19 through lens 18 at an exposure station generally designated 20, whereat the electrostatic latent image is formed on sensitive layer 12. At position 21 development of the electrostatic latent image takes place. Developer cloud supply 22 supplies a cloud of developer particles in gas to the area between layer 12 and development electrode 23 where development of the electrostatic latent image on layer 12 takes place. Although this embodiment is being shown using powder cloud development, it is to be realized that other means of development known to those in the art, as for example cascade development or the like, may be used and are intended to be encompassed by this invention. At the area generally designated 26 transfer of the developed image from layer 12 takes place. Roll 27 supplies a continuously fed web 28 under roller 30 and into contact with layer 12 whereat adhesive form of transfer occurs by using a web 28 having an adhesive coating on one surface thereof and applying proper pressure with roller 30. It is to be understood, of course, that other means of transfer may be used, such as corona transfer or the like, and this invention is intended to include such other means of transfer within its scope. The web, optionally, is next fed carrying the transferred image through the fusing apparatus wherein the copy is made permanent and then fed onto roll 36. The movement of web 28 is synchronized with the turning of drum 10, which in this embodiment is rotated in a clockwise direction. The drum 10 and the web 28 may be driven by a motor, as for example motor 9, or by other conventional means.

Although not shown in Fig. 1, a cleaning device may optionally be positioned along the path of rotation of the xerographic plate next following the transfer area to clean the plate surface prior to charging or sensitizing. The cleaning mechanism may be a rotating brush or the like to remove any particles remaining on the surface after transfer.

In Fig. 2 is shown a more detailed drawing of development stage 21. As in Fig. 1, the drum is generally designated 10 and the developer cloud supply is 22. The development electrode, designated 23 in Fig. 1, is herein designated 37 and 38. The developer cloud supply feeds developer through tubes designated 49, which are spaced from electrodes 57 and 38 by air stops 41 and 42, which may be composed of felt or some similar material. Tubes 40 may be capillary tubes or the like to flow a mixture of powder in gas turbulently to manifold 43 from the developer cloud supply. Turbulent flow through tubes of the proper tubular material will electrostatically charge the particles the desired amount and in the desired direction for deposition on the electrostatic charge pattern carried on the plate surface. Development electrodes 37 and 38 are, as shown in this embodiment, endless belts and they, due to their positioning, create manifold 43 which acts to diffuse the individual sprays of cloud or aerosol fed from individual tubes 40. It is to be realized, of course, that one or many tubes may supply the aerosol and diffusion through the manifold 43 creates a uniform cloud ofparticles in gas which is presented to the plate for development purposes. Air stops 41 and 42 act to prevent any back firing or back flowing of the cloud leaving tubes 40 and, thus, aid in forcing the cloud into the manifold 43 for proper diffusion before presentation to the charge pattern on the plate surface. Optionally, air stops 41 and 4 2 may have numerous fine holes to allow the supplying of additional air to the aerosol leaving the output end of tubes 43. The addition of air at this point has been found valuable in bringing about proper diffusion within manifold 43.

In this embodiment of the invention, drive means are shown for endless belt 38 and it is to be understood, of course, that similar mechanism or other mechanism known to the art may be used to drive endless belt development electrode 37. A motor 45, which is shown positioned centrally within belt 38 supplies driving powder through driving belts 46, 47, 48 and 50 to drive wheels 51, 52, 53 and 55. The driving belts may be connected to the axle of the driving wheels or other known means of connection may be used. A backing plate 56 is positioned between driving wheel 52 and driving wheel 55. Its ends, which are adjacent to the driving wheels, are recessed to allow free rotation of wheels 52 and 55. The driving wheels may present a friction type of surface to cause friction drive of belt 38, or they may at some point he sprocketed or the like to cause motion to be imparted from the wheels to the endless belt development electrode 33.

The lower section being made up of endless belt 37 also has driving Wheels, again designated 51, 52, 53 and 55, and a backing plate 56. The driving wheels are driven by any means known to those generally in the art to impart motion to endless belt development electrode 37.

Positioned somewhere along the path of movement of the development electrode is a cleaning mechanism. Two cleaning mechanisms are shown in this figure. In the upper section, rotating brush 57 is positioned to brush against endless belt 38. Surrounding brush 57 is a hood 58 connected to a vacuum cleaning mechanism, here shown as a vacuum cleaner and designated 60. In the lower section of this figure is shown a similar hood 58 connected to a vacuum cleaning mechanism designated 6t) positioned over and substantially enclosing a wiper blade 61. The wiper blade brushes against endless belt 37 and the cleaning mechanism draws off particles removed from the surface of the belt. Cleaning mechanism 60 in the upper section of this figure also draws off particles removed by brush 57. Cleaning mechanisms other than brush 57 or wiper blade 61 such as an air knife or the like may be used and are intended to be encompassed within the scope of this invention.

Backing plates 56 illustrate in this embodiment a magnetic material shaped to conform to the arc of the drum at a spacing which is equal throughout the area over which the backing plates are positioned. In operation developer is supplied through tubes 40 through manifold 43 and to the drum surface. The developer is supplied in a flowing stream and under pressure. Thus, on striking the drum surface, the developer will expand and flow along in both directions over the surface of the drum and between endless belts 37 and 38 and the drum surface. During operation driving means, as for example motor 45, move endless belts 37 and 38. Powder particles which fiow and deposit on the surface of the drum also tend to deposit on belts 37 and 38. Movement of the belts brings areas on which deposition has taken place into contact with the cleaning means, shown in this figure as brush 57 and wiper 61 whereat particles are removed from the belts and are drawn off by cleaners 60. Following cleaning, a clean belt portion is moved to the area above drum 10.

Proper spacing of the endless belt from the surface of invention to be limited to such a construction.

drum is necessary to produce high quality xerographic images. This is accomplished in this embodiment through the use of backing plates 56 composed of magnetic materials. The belts 37 and 38 are in this embodiment either completely composed of a material affected by the magnet or coated with a material affected by the magnet and when moved over magnetic backing plates 56, they adhere through magnetic attraction to the surface of backing plates 56 and to the path they are to follow, thus attaining proper spacing of the development electrodes 37 and 38 from the surface of drum 10.

Reference is now had to Fig. 3 wherein a section taken along line 3-3 of the lower section of Fig. 2 is shown in detail. As in Fig. 2, 56 designates the magnetic backing plate, 37 the endless belt development electrode, and 10 the drum. Positioned at the edges are guides 62 which further aid in positioning the development electrode 37 in its proper position and at a proper distance from the surface of drum 10. Since the path of the endless belt development electrode is concave when over the drum surface guides 62 are desirable to aid in shaping the belt. Between endless belt 37 and drum 10 is an air gap, herein designated 63.

Reference is now had to Fig. 4 wherein is shown a section of another embodiment of driving means and positiouing means for an endless belt development electrode. In this figure, as in Fig. 2, the endless belt is again desiguated 3%. However, in this figure, instead of a magnetic backing plate, a number of individual roller wheels 65 are shown as the spacing and backing element of the development electrode 33. Each of these rollers 65 is preferably magnetic, and thus, they draw to themselves through magnetic forces endless belt 38, thereby causing proper positioning of the belt as it passes over the surface of drum 10. The driving means for the endless belt of this embodiment may comprise driving means as shown in connection with Fig. 2 or may, in addition, comprise driving means which supply movement to each of rollers 65. A particular advantage found in connection with the use ofmagnetic rollers as distinguished from a magnetic solid plate, is that forces working on the endless bel-t tending to draw the belt taut and thus straight rather than concave as it passes over the surface of drum 1d, are overcometo a greater extent. Portions of the belt adhering through magnetic attraction to portions of the roller tend to roll with the roller, and thus, tend to balance out the forces tending to pull the belt straight.

Reference is now had to Fig. 5 wherein another embodiment of this invention is shown. Driving wheels similar to the driving means shown in Fig. 2 are used, or other mechanism may be used to cause movement of the endless belt. In this embodiment, the belt is positioned in a spaced relationship from the surface of drum 10 through the use of negative pressure supplied to hood 66 from negative pressure generator 67. Hood 66 has a guide face 68 having many fine holes throughout its surface to supply the suction necessary to hold the belt, herein again designated 33, in position. Preferably, when negative pressure is being used to position the belt at a proper distance from the surface of drum 10, the belt itself should be substantially air impervious. This is desirable to prevent the movement of powder cloud through the belt and out of the effective area for development and also to assure proper positioning of "the belt against guide face 68.

It is to be realized, of course, that the use of a negative pressure to hold the belt in place may be combined with the use of magnetic rollers or a magnetic plate having holes formed therein, and that such a combination is intended to be encompassed by this invention.

Although the embodiments shown and discussed in connection with Figs. 1 through 5 have considered drum 10 as the xerographic plate, there is no desire in this There exist in the art of xerograp'hy flexible plates which may be supplied in web or roll form. The backing menibers of such flexible plates are in practice kept in contact with a conductive member during the steps of the xerographic cycle from charging to the developed image, although such contact is not necessary for all steps of the process. Whether in contact with a conductive member of a non-conductive member, it is still desirable to maintain contact between the flexible xerogr-aphic plate and a solid guide and positioning base during the development stage to maintain proper spacing between the development electrode and the surface being developed. Thus, it is to be realized that a flexible xerographic plate could be positioned against the surface of a drum during the development stage and in such an instance the drum 10 discussed in connection with the previous embodiments of this invention would act simply as a guide and positioning solid base rather than the plate member itself.

It is also possible in the art of xerography to develop an existing electrostatic image on a plate on a material placed in contact with the plate surface during the development cycle. Such development is disclosed in Carlson Patent No. 2,297,691, Fig. 9, and the use of a development electrode during such development substantially improves quality of the end product. It is intended to include within this invention the use of a sheet or web or the like placed in contact with the surface carrying the electrostatic charge pattern during development while an endless belt development electrode is positioned in the development zone.

Reference is now had to Fig. 6 wherein is shown another embodiment of this invention. In this embodiment endless belt development electrode 70 is caused to move by driving wheels 71 and 72 and is positioned at its proper distance from the plate by magnetic backing plate 73. The plate 75 in this embodiment is a flexible plate which is charged and exposed and then fed into spaced parallel relationship with the endless belt development electrode 70 for development purposes. Movment of the belt is accomplished by driving wheels 76, 77 and 78. A cloud of developer particles is fed from aerosol nozzle 80 to the area between the development electrode and the flexible plate 75. In this embodiment the development electrode is shown formed as a single section, but it is to be understood that it could be formed as a double section as, for example, is shown in Fig. 2, and the supply of developer could be fed from a nozzle through a manifold as shown in Fig. 2. Also included in this embodiment is rotating brush 81 to wipe free the surface of development electrode 70 for removal by a vacuum creating means or the like. Flexible plate 75 is preferably held in a flat position during development through the use of a pressure hood 82 supplied with negative pressure by a pressure generator 83. A flat face plate 85 having many fine holes formed therein is positioned in the front end of the hood and at the surface to hold plate 75 flat.

It is also to be realized that the flexible plate 75 could in this embodiment be a conductive metal support and that a flexible web of xerographic material could be pressed against the surface of conductive material 75 and into the development zone for development purposes or a web or the like may be positioned on the plate surface, as discussed above in connection with the previous embodiments.

Reference is now had to Figs. 7, 8 and 9, wherein is shown an embodiment of guide and positioning mechanism for the endless belt development electrode. The endless belt development electrode in Figs. 7 and 8 is designated 38, as in previously discussed figures. Attached to the edges of the endless belt are arms 86 which terminate in buttons 87. Arms 86 are joined to one another by links 88 of a continuous chain. The chain links 88 pull the endless belt development electrode 38 taut in one direction whereas the buttons 87 ride in guide rails 90 to pull the endless belt development electrode 38 taut in the other direction. In Fig. 9 one guide rail 90 is shown positioned in respect to a drum 10. The guide rail 90 is shaped to conform with the path through which the development electrode is led. Links 38 may be formed in the shape of a ladder type of chain and sprockets to drive the development electrode through the ladder chain may be used to cause movement of the development electrode through its cycle.

Optionally, there may he provided a seal between the edges of the plate and the guide rail 90 for the endless belt development electrode to prevent leakage of powder cloud out the edges of the plate to be developed. A similar seal could be provided between the plate and the endless belt development electrode shown in Fig. 2. Such a seal will act to feed the powder cloud along the length of the plate and will prevent leakage around the edges.

The use of means to pull the development electrode taut has been found desirable when a flexible electrode is used. Such means aid in shaping the electrode and thus positioning it at a proper and equal distance from the surface to be developed. Accurate and equal spacing has been found desirable when high quality xerographic development is the objective.

The endless belt being discussed herein should be flexible to allow it to move through its cycle which includes turns and changes of direction. When either a magnetic backing plate or magnetic rollers, or a combination of these two, is being used to cause movement of the endless belt development electrode through its proper path at a proper distance from the surface of the plate, the development electrode should include a magnetic material. When a vacuum or negative pressure system is being used to shape the development electrode during its travel, preferably a substantially air impervious material should be used. In all instances, a material which is a fair conductor of electricity is necessary, in that generally the electrode will be biased to the potential of the plate backing member or at a potential raised therefrom during development. This is intended to include within the scope of this invention cloth carrying a metal layer, cloth having interspersed throughout sputtered metal, plastic carrying a metal layer, foil, stiff but flexible metal (which will be valuable to prevent undesirable buckling), and the like. The development electrode should be dimensionally stable and should be polished when possible so as to present a smooth, even, equidistant surface to the photoconductive insulating layer. In forming a development electrode according to this invention, it is preferred that means be provided to vary spacing. Generally the electrode will be spaced at from .1 to .001 inch from the photoconductive insulating layer and screw adjustments or the like may be connected to the supporting elements of the means which position the electrode from the surface of the plate, such as the magnetic backing plate or the vacuum or negative pressure face or the rollers, or combinations of these, to vary the spacing.

It is to be realized that the endless belt development electrode may be moved at varying linear rates of speed and that faster speeds are generally preferred in that a portion of the belt would be carried through the entire cycle with greater rapidity than if slow speeds were used. In carrying the belt through its cycle, the belt is cleaned by the cleaning means and is then carried to the development zone. Preferred timing for movement of a portion of the development electrode from the point when that portion enters the zone in which development will take place to the point when the portion leaves the development zone is less than three minutes for high quality continuous tone Xerographic reproductions. For line copy work, slower speeds are possible.

The area the development electrode should cover over a plate should be such that loss of developer cloud from extremities is effectively prevented due to deposition on the plate and the slot or the manifold between the two development electrodes when present through which the aerosol of powder particles is sprayed should be positioned as near to the center as possible.

While there has been described what at present is considered to be a preferred embodiment of the invention, it is to be understood that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the appended claims to cover all such modifications as fall within the true scope of the invention.

What is claimed is:

1. In a xerographic apparatus, the combination comprising a cylindrical xerographic plate with an external photoconductive insulating layer, a backing plate having a concave surface positioned at a slight distance from the surface of the xerographic plate and shaped to conform to the configuration of that portion of the surface of the xcrographic plate over which it is positioned, an endless electrically conductive belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the backing plate, said electrode while in the area of contact with the concave surface of the backing plate being spaced apart from the surface of the xerographic plate, means to apply a xerographic development cloud in the space between said development electrode in area contact with the backing plate and the surface of the Xerographic plate, cleaning means positioned along the path of movement of the endless belt development electrode at a point removed from the surface of the xerographic plate, and driving means to move said electrode through said path, said backing plate having means to cause said electrode to conform to the configuration of its surface.

2. In a Xerographic apparatus, the combination comprising a cylindrical Xerographic plate with an external photoconductive insulating layer, backing means having a concave surface positioned at a slight distance from the surface of the Xerographic plate and shaped to conform to the configuration of that portion of the surface of the Xerographic plate over which it is positioned, an endless belt development electrode formed of electrically conductive material positioned to move through a path which includes an area of contact with the backing means, a brush positioned along the path of movement of the endless belt development electrode at a point removed from the surface of the Xerographic plate to clean the endless belt development electrode, means to spray an aerosol of powder particles into the area between the endless belt development electrode and the surface of the xerogra-phic plate at that portion of the path of the endless belt development electrode whereas said electrode is in contact with the backing means, and driving means to move the electrode through its path, said backing means being magnetic and said electrode being formed of magnetically affected material to thereby cause said electrode to conform to the configuration of the backing means.

3. In the method of developing by making visible electrostatic charge patterns on the surface of a Xerographic plate in an automatic cylindrical plate machine, the improvement comprising continuously moving during development an electrically conductive magnetically affected endless belt development electrode in a path which includes an area of contact with a magnetic backing plate in close uniform proximity with the Xerographi'c plate, spraying an aerosol of powder particles during development to the area between the development electrode and the surface of the Xerographic plate at the portion of the path of the development electrode which is in contact with the magnetic backing plate, and cleaning deposited powder particles from the surface of the endless belt development electrode at a point along its path removed from the surface of the xerographic plate.

4. In a Xerographic apparatus, the combination comprising a cylindrical Xerographic plate with an external photoconductive insulating layer, backing means having a concave surface positioned at a slight distance from the surface of the xerographic plate and shaped to conform to the configuration of that portion of the surface of the xerographic plate over which it is positioned, an endless belt development electrode formed of electrically conductive material positioned to move through a path which includes an area of contact with the backing means, a brush positioned along the path of movement of the endless belt development electrode at a point removed from the surface of the xerographic plate to clean the endless belt development electrode, means to spray an aerosol of powder particles into the area between the endless belt development electrode and the surface of the xerographic plate at that portion of the path of the endless belt development electrode positioned between the backing means, and driving means to move the electrode through its path, said backing means being adapted to cause said electrode to conform to the configuration of its surface through the use of negative pressure and said electrode being substantially impermeable to air.

5. In a xerographic apparatus, the combination comprising a rotatable cylindrical xerographic plate carrying a photoconductive insulating layer on its outer surface, a first and second fixed backing plate each having a concave surface closely and uniformly spaced from the xerographic plate and each backing plate positioned adjacent to the other, a first conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the first backing plate, a second conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the second backing plate, the paths of said development electrodes further including a region extending from the adjacent ends of said backing plate and in which the electrodes are in a spaced apart relation defining a channel extending to the surface of the xerographic plate, powder supply means to spray an aerosol of powder particles into said channel toward said plate, cleaning means positioned along the path of movement of each endless belt development electrodevat a point removed from the surface of the xerographic plate, and means to drive each of said electrodes through their respective paths, said backing plates having means to cause said electrodes to conform to configurations of their surfaces.

6. -In a xerographic apparatus, the combination comprising a rotatable cylindrical xerographic plate carrying a photoconductive insulating layer on its outer surface, a first and second fixed backing plate each having a concave surface closely and uniformly spaced from the xerographic plate and each backing plate positioned adjacent to the other, a first conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the first backing plate, a second conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the second backing plate, the paths of said development electrodes further including a region extending from the adjacent end-s of said backing plate and in which the electrodes are in a spaced apart relation defining a channel extending to the surface of the xerographic plate, powder supply means .to spray an aerosol of powder particles into said channel toward said plate, cleaning means positioned along the path of movement of each endless belt development electrode at a point removed from the surface of the xerographic plate, and means to drive each of said electrodes through their respective paths, said backing plates being magnetic and 10' said electrodes being formed of magnetically affected materials thereby causing said electrodes to conform to the configurations of the concave surfaces of the back ing plates.

7. In a xerographic apparatus, the combination comprising a rotatable cylindrical xerographic plate carrying a photoconductive insulating layer on its outer surface, a first and second fixed backing plate each having a concave surface closely and uniformly spaced from the xerographic plate and each backing plate positioned adjacent to the other, a first conductive endless belt de velopment electrode positioned to move through a path which includes an area of contact with the concave surface of the first backing plate, a second conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the second backing plate, the paths of said development electrodes further including a region extending from the adjacent ends of said backing plate and in which the electrodes are in a spaced apart relation defining a channel extending to the surface of the xerographic plate, powder supply means to spray an aerosol of powder particles into said channel toward said plate, cleaning means positioned along the path of movement of each endless belt development electrode at a point removed from the surface of the xerographic plate, and means to drive each of said electrodes through their respective paths, said backing plates being adapted to cause said electrodes to conform to the configurations of their surfaces through the use of negative pressure and said electrodes being substantially impermeable to air.

8. In a xerographic apparatus, the combination com prising a rotatable cylindrical xerographic plate carrying a photoconductive insulating layer on its outer sur-- face, a first and second fixed backing plate each having a generally concave surface closely and uniformly spaced from the xerographic plate and each backing plate positioned adjacent to the other, a first conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the first backing plate, a second conductive endless belt development electrode positioned to move through a path which includes an area of contact with the concave surface of the second backing plate, the paths of said development electrodes further including a region extending from the adjacent ends of said backing plate and in which the electrodes are in a spaced apart relation defining a channel extending to the surface of the xerographic plate, powder supply means to spray an aerosol of powder particles into said channel toward said plate, cleaning means positioned along the path of movement of each endless belt development electrode at a point removed from the surface of the xerographic plate, and means to drive each of said electrodes through their respective paths, said concave backing members each comprising a plurality of magnetic rollers and said electrodes being formed of electrically conductive magnetically affected material thereby causing said electrodes to conform to the configuration of the backing members.

References Cited in the file of this patent UNITED STATES PATENTS 1,362,518 Villiers Dec. 14, 1920 2,573,881 Walkup et a1 Nov. 6, 1951 2,636,471 Starkey Apr. 28, 1953 2,725,304 Landrigan et a1. Nov. 29, 1955 2,752,833 Jacob July 3, 1956 2,756,676 Steinhilper July 31, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent-No. 2,844,123 July 22, 1958 Richard E Hayford It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 38, for vMovment" read --Movement--; column 8, line 48 for "whereas" read =--whereat=-; same column 8, line 55, beginning with "3. In the" strike out all to and including "plate." in line '71, which comprises claim 3; the claims now numbered 4, 5 6, '7 and 8 should be renum= bered 3, 4, 5, 6 and 7, respectively; in the heading to the printed specification, line 7, for "'8 Claims" read --=='7 Claims--.

Signed and sealed this 14th day of October 1958.

(SEAL) Attest:

KARL H. AXLINE Attesting Ofiicer ROBERT C. WATSO] Commissioner of Pate:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent-No. 2,844,123 July 22, 1958 Richard E Hayford It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 38, for vMovment" read --Movement--; column 8, line 48 for "whereas" read =--whereat=-; same column 8, line 55, beginning with "3. In the" strike out all to and including "plate." in line '71, which comprises claim 3; the claims now numbered 4, 5 6, '7 and 8 should be renum= bered 3, 4, 5, 6 and 7, respectively; in the heading to the printed specification, line 7, for "'8 Claims" read --=='7 Claims--.

Signed and sealed this 14th day of October 1958.

(SEAL) Attest:

KARL H. AXLINE Attesting Ofiicer ROBERT C. WATSO] Commissioner of Pate:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent-No. 2,844,123 July 22, 1958 Richard E Hayiord It is hereby certified that error appears in the printed specification of theabove numbered patent requiring correction and that the said Letters Patent should read as corrected below.-

Column 6, line 38, for "Moment" read -=-Mov ement--; column 8, line 48 for "whereas" read =--whereat--; same column 8, line 55, beginning with "3. In the" strike out all to and including "plate." in line '71, which c.0m prises claim 3; the claims now numbered 4, 5, 6, 7 and 8 should be renum bered 3, 4, 5 6 and 7, respectively; in the heading to the printed specification, lin'e 7, for "8 Claims" read '7 Claims-.

Signnd and sealed this 14th day of October 1958.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSO] Atteeting Officer Commissioner of Pate: 

